In this study, for the first time, {111} facet exposed anatase TiO2 single crystals are prepared via both F– and ammonia as the capping reagents. In comparison with the most investigated {001}, {010}, and {101} facets for anatase TiO2, the density functional theory (DFT) calculations predict that {111} facet owns a much higher surface energy of 1.61 J/m2, which is partially attributed to the large percentage of undercoordinated Ti atoms and O atoms existed on the {111} surface. These undercoordinated atoms can act as active sites in the photoreaction. Experimentally, it is revealed that this material exhibits the superior electronic band structure which can produce more reductive electrons in the photocatalytic reaction than those of the TiO2 samples exposed with majority {010}, {101}, and {001} facets. More importantly, we demonstrate that this material is an excellent photocatalyst with much higher photocatalytic activity (405.2 μmol h–1), about 5, 9, and 13 times that of the TiO2 sample exposed with dominant {010}, {101}, and {001} facets, respectively. Both the superior surface atomic structure and electronic band structure significantly contribute to the enhanced photocatalytic activity. This work exemplifies that the surface engineering of semiconductors is one of the most effective strategies to achieve advanced and excellent performance over photofunctional materials for solar energy conversion.

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Recent theory has found that native defects such as the O vacancy V(O) and Zn interstitial Zn(I) have high formation energies in n-type ZnO and, thus, are not important donors, especially in comparison to impurities such as H. In contrast, we use both theory and experiment to show that, under N ambient, the complex Zn(I)-N(O) is a stronger candidate than H or any other known impurity for a 30 meV donor commonly found in bulk ZnO grown from the vapor phase. Since the Zn vacancy is also the dominant acceptor in such material, we must conclude that native defects are important donors and acceptors in ZnO.

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SrTiO 3 is a promising photocatalyst for the production of hydrogen from water splitting under solar light. Cr doping is an effective treatment for adjusting its absorption edge to the visible-light range, although the performance of Cr-doped SrTiO 3 is strongly affected by the oxidation number of the Cr ions. In this study, we theoretically predict that elevating the Fermi level, i.e., n-type carrier doping in SrTiO 3 , can stabilize the desirable oxidation number of chromium (Cr 3+), contributing to a higher activity for H 2 evolution. Our computational results, based on hybrid density-functional calculations, reveal that such an n-type condition is realized by substituting group-V metals (Ta, Sb, and Nb), group-III metals (La and Y), and fluorine atoms for the Ti, Sr, and O sites in SrTiO 3 , respectively. From our systematic study of the capability of each dopant, we conclude that La is the most effective donor for stabilizing Cr 3+. This prediction is successfully evidenced by experiments showing that the La and Cr codoped SrTiO 3 dramatically increases the amount of H 2 gas evolved from water under visible-light irradiation, which demonstrates that our guiding principle based on Fermi level tuning by the codoping scheme is valid for the design of advanced photocatalysts.

Using hybrid density-functional calculations we investigate the effects of native point defects on the electrical and optical properties of In 2 O 3. We analyze formation energies, transition levels, and local lattice relaxations for all native point defects. We find that donor defects are in general more energetically favorable than acceptor defects, except near O-rich conditions, where oxygen interstitials and indium vacancies have low formation energy in n-type In 2 O 3. The oxygen vacancy is the lowest-energy donor defect with transition level (2+/+) slightly below and (+/0) slightly above the conduction-band minimum (CBM), with a predicted luminescence peak at 2.3 eV associated with the transition V 0 O → V + O. Despite being a shallow donor, the oxygen vacancy becomes electrically inactive for Fermi levels at or higher than ∼0.1 eV above the CBM. This indicates that conductivity due to oxygen vacancies will saturate at rather low carrier concentrations when compared to typical carrier concentrations required for transparent conducting oxides in many device applications.

We used hybrid density-functional calculations to clarify the effect of substituting chromium for titanium (Cr(Ti)) on photocatalytic activities of Cr-doped SrTiO(3). A singly negative Cr(Ti)⁻, which is relevant to a lower oxidation state of Cr, is advantageous for the visible light absorption without forming electron trapping centers, while other charge states are inactive for the photocatalytic reaction. Stabilizing the desirable charge state (Cr(Ti)⁻) is feasible by shifting the Fermi level towards the conduction band. Our theory sheds light on the photocatalytic properties of metal-doped semiconductors.